


Soul Tap

by Askellie (NadaNine)



Category: Undertale (Video Game)
Genre: Abuse of Authority, Biting, Character Turned Into Vampire, Horror, Implied/Referenced Rape/Non-con, M/M, Mild Gore, Mind Control, Vampires, Violence
Language: English
Status: Completed
Published: 2016-09-11
Updated: 2016-09-11
Packaged: 2018-08-14 10:25:27
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence, Rape/Non-Con
Chapters: 1
Words: 7,932
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8010040
Author URL: https://archiveofourown.org/users/NadaNine/pseuds/Askellie
Summary: <blockquote class="userstuff">
              <p>Working with the Royal Scientist is not quite what Sans expects.</p>
            </blockquote>





	Soul Tap

**Author's Note:**

> Dedicated to Sweetsinnerchild, who expressed an interest in seeing some Vampire!Gaster action. :9

Working with the Royal Scientist is not quite what Sans expects.

The work itself is amazing, of course. It's complex, fast-paced and exciting. He's working harder than he ever has before, and while in most instances the prospect of work leaves him uninspired, this is exactly the kind of challenge he enjoys; bending the equations to his whims and making them give up their hidden answers. It's a hell of a lot more thrilling than picking up his laundry whenever Pap nags him, that's for sure.

The people, though...

It's weird. Sans has known all kinds of scientists – his teachers, fellow students, the few independents he'd had to interview for projects or intern with for experience – but the Royal Scientists' personal team are...different. And even more bizarrely, they're all different in the same way. There's a strange kind of gloom that seems to hang over every one of them, a heavy cloud of exhausted malaise. Each one of them is known for their brilliance - a stand out in their field of choice - but when working together there's only a strangely subdued and quiet unity that's almost robotic. There's rarely any conversation, no friendly chats, no arguments, even. Sans has never seen anything like it.

They do good work, though, and he starts to wonder if maybe _he's_ the one who doesn't get it. This is the team that put together the Core, after all. They survived the darkest days of monster history. Maybe it's natural that they're a little more reserved than Sans is used to. Their silent, mechanical synergy gets things done, so it's not really a _problem_ , per se...

Still, Sans tries to ignite a little more humour on a daily basis. Every so often he's successful. A timely joke or a particularly awful pun will startle a laugh out of someone, and for a moment it's like the spark of life returns to them and he'll have something almost like a normal conversation for a change. It doesn't last long, but it's enough to assuage his fears that there's nothing really wrong here, despite the quiet nagging of his instincts. It's just his imagination.

It does worry him, though, that his light-hearted banter might mark him as being a poor fit for the rest of the team, so it's particularly nerve-wracking to find himself being summoned directly to Gaster's office after one especially long, frustrating day. His current equations aren't panning out as he hoped, and he might have accidentally fallen asleep at his desk again after staying up all of the night before trying and failing to find a better solution. At best, he's expecting a reprimand. At worst, he's gonna have to fast-talk his way out of being fired.

He's seen very little of Gaster himself since coming to the Royal Labs, so it surprises him how strangely welcoming he is when he greets Sans with a genial smile and indicates for the skeleton to take a seat.

“My apologies, Sans,” Gaster says sincerely, taking his own place behind the desk. “I know you're our newest team-member, but I'm afraid I haven't had much of a chance to get to know you personally.”

“No worries, Doc,” Sans replies, slouching comfortably. “Everyone knows you're busy.”

For a monster with such an intimidating reputation, Gaster is surprisingly amicable. There's an alluring vibrancy to him as he talks to Sans about some of their ongoing projects, making no mention of all about the hold-ups on Sans's part. He'd wondered if the odd despondency in the rest of the team had come about from the others matching their temperaments to better suit their boss, but Gaster is lively and jovial. He laughs at Sans's jokes. His warm smile makes Sans feel important. He can't help but feel pangs of loyalty and admiration for this man.

It's enough that he can ignore the way his soul is pounding against the inside of his sternum. He can't quite place exactly why, but despite his open demeanour there's something about his boss that his body responds to instinctively. Gaster is powerful, there's no denying that. The tingle of his magic in the air isn't wholly suppressed, and Sans feels it wash over him, prickling oddly on his bones. It feels a little uncomfortable to be so immersed in it, breathing it in as they talk, but Gaster seems oblivious so Sans assumes he must not realise he's doing it.

Then there's the aura of his LOVE...Sans deliberately doesn't examine it too closely even though he's one of the few monsters who can get an accurate read on it. It's not exactly unexpected. Even Asgore has some LOVE, and everyone knows the King is one of the kindest, gentlest souls in the kingdom. Most monsters who survived the war gained at least a little, and Sans isn't going to judge their choices. Even without close examination, he suspects Gaster has the highest of anyone he's ever met, but then again rumour has it that Gaster helped create weapons for use against the humans. As any proper scientist would, Gaster probably tested them himself first, so there's no way Sans could hold that against him.

“I'm really looking forward to seeing more of your contributions to the team, Sans,” Gaster tells him earnestly, and Sans blinks. He must have lost the thread of the conversation at some point, too distracted by his thoughts, because suddenly Gaster isn't on the other side of the desk. He's right next to Sans, leaning over him. His voice is soft, hypnotic. The lights in his eyes are usual pale and white, like Sans's, but at the moment there's a distinct hue of purple to them. Sans's soul twists in his chest. “In fact, perhaps you could take me over your equations now?”

He reaches for Sans, and without any concious thought whatsoever Sans ducks out from under his hand and is suddenly halfway across the room. Gaster blinks at him in surprise, and Sans can only stare dumbly back, his bones almost rattling from nerves, his stance poised to flee from some unknown threat.

...Shit, what the hell is he doing? It's just Gaster. Sans tries to maintain his composure, as if he can pretend like he hasn't just flinched away like he was worried his boss was going to assault him. “Uh...maybe later, Doc. I have to...get home.”

“You're leaving?” Is it just his imagination or is there a hint of flat displeasure in Gaster's voice. No, he must be imagining it. It's probably just disappointment. They'd been having such a good chat, after all.

“Y-yeah, my brother gets real cranky if he doesn't get his bedtime story, you know?” Sans tries to grin, but it feels forced. What the hell is wrong with him? He tries to be discreet about checking the door behind him, suddenly worried it might be locked, wondering if he can reach it before Gaster could catch him--

\--wait, what? What the fuck?

His irrational and completely unfounded fears prove to be exactly that. Gaster suddenly smiles at him, banishing all semblance of displeasure.

“Yes, of course. Your family comes first. Thank you so much for taking the time to speak with me, Sans.”

Sans releases a breath he hadn't known he was holding, managing a slightly more sincere grin. “Yeah, sure. It was great, doc! We should do it again sometime.”

It isn't that he's fleeing from Gaster's office, he tells himself. He's just in a hurry to get home to his brother.

* * *

“SANS?”

Sans starts, glancing towards his brother's pouting expression. Papyrus looks pointedly down at the book on Sans's lap. “YOU DIDN'T FINISH THE STORY.”

“Oh! Sorry, bro.” Sans scrubs hard at his eyesockets, cursing his failing concentration. He hasn't been able to focus all evening. Every time his mind wanders, all he can see is Gaster's intense, violet eyes and his kind smile, like the image has been imprinted on the inside of his skull.

“Are you okay?” Papyrus asks, looking more concerned. Some would say he's probably too old for bedtime stories, especially those of Fluffy Bunny's calibre, but it's not really about the book as it is about the ritual. Sans treasures these moments with his brother, and he knows Papyrus feels the same. It's frustrating that Gaster's presence is disturbing their usual routine.

“Just a long day,” Sans shrugs, nestling closer to Papyrus. His brother's larger body is protective and comforting, chasing off the lingering ghost of fear that had followed him out of Gaster's office. “It's nothing to be worried about.”

He hopes that's true. Whatever it is about Gaster that riles him up should be easy to avoid. The man rarely comes out of his office except for the occasional inspection, so Sans should have some time to master his stupid instincts before it becomes an issue.

* * *

“Sans, can you come with me, please?”

The powers that be – which, in this instance, is Gaster himself – are not on Sans's side. He's spent the whole day at his desk, making a point of being immersed in quiet, diligent work so as to be as discreet as possible. Apparently that wasn't enough to escape Gaster's notice. Sans quietly frets, wondering what sort of explanation he can offer if Gaster decides to ask him about his strange behaviour yesterday.

Except that this time instead of being taken into Gaster's office, he's led into his boss's private laboratory. He can't help but feel awed. The lab is well funded by the King, of course, but Gaster's personal equipment has been amassed over the entirety of his (reportedly considerable) lifespan. There's a small scale model that Sans thinks must have been one of the original prototypes of the core. A wall full of books takes up one wall completely, and Sans finds himself entranced by the sheer variety in the titles and how well they've been preserved. Most fascinatingly, from the ceiling hangs an ornate diorama of the solar system, apparently crafted to scale. The central sun actually casts light on the orbiting planets in a dazzling display that keeps Sans thoroughly entranced until Gaster's deep chuckle breaks him from his daze. He flushes slightly, abashed, but Gaster only seems amused.

“Do you like it?”

“It's amazing,” Sans replies without reservation. His knowledge of the stars and planets is mostly theoretical, and heavily based on physics, but he's always imagined that the sheer majesty of those massive celestial bodies must be beautiful to witness. Even if the diorama only captures a hint of that brilliance, he's awed.

Gaster seems honestly pleased by his reaction. “I'm glad. Most others find reminders of the sky too painful, but I would prefer not to lose sight of what we have lost.”

There's a quiet, almost peaceful moment as they both stare up at the slow revolution of planets. Sans finds himself much more at ease this time, and is relieved. Maybe he's gotten used to the heavy blanket of Gaster's magic prickling at his senses. It probably helps that the man seems to be keeping his respectful distance, giving Sans time to adjust.

“What can I do for you, Doc?” Sans asks after some time. As much as he'd like to keep admiring the ceiling indefinitely he's pretty sure that isn't the reason Gaster called him here.

“Ah, well. As it happens, I'm about to begin a new experiment that will require a bit of additional handling,” Gaster said, eyeing Sans with a bright intensity that was hard to look away from. “I was hoping I could ask you to assist me for the duration of the project.”

Sans bit down on the immediate, fervent agreement that he wanted to express, though he wasn't quite sure why. Wasn't it an absolute honour, for Gaster to choose him over anyone else? Wasn't this the kind of moment every budding scientist dreamed about?

Instead, his tone was wary, almost a little suspicious, as he asked, “Why me? I mean, you've got a whole bunch of great people here with more experience.”

“I like to get to know all the members of my team personally,” Gaster told him with an indulgent smile. His eyes were holding Sans's again. The odd purple tint was back. “Besides, you're young and brilliant...I think this could be an excellent opportunity for you to prove yourself.”

“Aw, shucks, Doc,” Sans says, and he wants to look away in abashment at the flattery, he really does, but it's hard when Gaster is looking at him like that. Like he's something as fascinating and beautiful as the model on the ceiling. That feels...it doesn't feel right, but Sans can't quite articulate why even in his own thoughts.

“Come with me,” Gaster says, reaching out a hand. Sans tries to focus on it, on the long, elegantly pale fingers, the strange circular voids in the palms, but his gaze is almost immediately drawn back to Gaster's face as if by magnetism. “Let me show you what we'll be working on.”

Sans finds his hand beginning to reach out all on its own, and forcibly stops it in the air. Some tiny voice inside him is telling him that this is a bad idea, that something wrong is afoot, but-

_**TAKE MY HAND, SANS.** _

His hand completes its arc, landing in Gaster's outstretched fingers, which close over his companionably, as if they are sharing nothing more than a businesslike handshake. Sans is ready to berate his over-active instincts again as Gaster smiles at him and--

things

become

very

unclear.

\-- _he's snarling and swearing and reaching instinctively for his magic but he's so dizzy, he can't concentrate--_

_\--there's a hand on his skull, petting him gently as his face is pressed up against the front of Gaster's jacket. He's never been close enough to smell the guy, that would just be weird...wait, this is weird, what is he doing? His face is wet and his eyesockets hurt for some reason. Has he been crying? What...?--_

_\--His face is pressed against one of the tabletops, cushioned atop a series of reports. He thinks he must have fallen asleep except that there's something heavy on his scapula, holding him down._

“ _How does it feel, Sans?” Gaster asks him, his voice a soft purr._

“ _Hurts,” Sans croaks weakly, but he doesn't know what he's saying because he feels something distantly that thrusts him hard against the table and it's not pain that makes him gasp out, “More!”--_

– “I'm very proud of you.”

Sans sways on his feet, feeling like he's about to fall over. “W-what?”

Gaster's hand is on his shoulder. He stares at it numbly, feeling like he should be responding to that in some way, but his body doesn't seem to want to move much. “You worked very hard. I can see you'll be an asset to the lab. Go home and get some sleep, okay, Sans?”

Home. Sleep. Those two things sound absolutely amazing right now. “Y-yeah.”

He wanders off vaguely, not even saying goodbye, but that's okay. He just has to...get home. He did a good job. Everything is fine.

Sans spends almost half an hour lost in the corridors even though he knows them all like the back of his hand. He just can't figure out how to get back to his desk, or how to get to the exit. Eventually one of the other scientists has to kindly escort him out, and Sans spends a moment stupidly wondering why he needed to do that in the first place when he could just have taken a shortcut straight home in the first place.

He steps from the shadow outside the labs into his own living room and immediately passes out on the couch, oblivious to the startled cry of his brother who had spent the last four hours waiting up for him.

* * *

“SANS?! SANS WAKE UP PLEASE!”

It's the note of desperation in his brother's voice that finally rouses him. Sans sits up groggily, clumsily shooing away Papyrus's worried, fluttering hands. “Ugh. What time is it?”

“IT IS MORNING! BUT SANS, YOU CAME BACK SO LATE AND YOU SLEPT SO DEEPLY I COULDN'T WAKE YOU UP! ARE YOU-?”

“Crap, I need to get to work,” Sans mumbles, checking the time on his phone, aghast. He's definitely running late.

“BUT BROTHER-!”

“Sorry, Pap! Can we talk later? I gotta go.”

He's stumbling out the door, heedless of his brother calling after him, “SANS, YOU HAVEN'T EVEN CHANGED YOUR CLOTHES OR SHOWERED. HOW CAN YOU-! AUGH! SANS!!”

* * *

Thankfully no one comments about his tardiness, nor his sloppy state of dress. He tries to work extra hard all morning to make up for it, but he's not sure anyone even notices. He wonders if maybe Gaster told them how he'd stayed late and they're all making a point to go easy on him. The idea puts a dumb, infatuated smile on his face. Gaster is really a great boss.

The day passes without him being fired. He goes home and apologises to his brother. Tells him that it was a tough, last-minute project, but brags a little about being chosen personally by the Royal Scientist. Papyrus seems honestly excited for him.

“So what are you doing?” Papyrus asks eagerly, leaning over the table. They're eating his spaghetti which normally can only barely be defined as edible, but tonight Sans eats like it's going out of style. He's absolutely starving in a way he hasn't been since the early days of training with his magic.

“We...” Sans pauses, frowning slightly, rubbing at his collarbone. He should know the answer. Gaster spoke to him about it at length, he just...he can't recall a single thing about it. It bothers him, but he doesn't want Papyrus to know so he grins playfully. “Aw, bro. Sorry, it's confidential. Royal Scientist stuff. Very hush hush.”

Papyrus looks even more impressed with this answer. “Wowie!”

He doesn't remember much of the previous evening, but it's fine. Things at the lab have been busy, Gaster's lab had been overwhelming...he'll figure it out without giving Papyrus any ammunition to tease him with about getting old enough to suffer from memory loss.

* * *

Gaster's laboratory is just as impressive as the first time. Sans hovers in the doorway, just taking minute to admire the solar system diorama overhead. No wonder he hadn't been able to keep his thoughts straight after witnessing such an amazing thing. It's downright hypnotising, the way the planets slowly revolve above him, each spinning independently to simulate their own daylight cycles as well as the orbital paths. He could stare at it all day.

“Welcome back, Sans,” Gaster says, straightening up from where his lanky frame had been elegantly bent over one of the benchtops. His body is swathed in shadow. Sans wonders why he doesn't turn up the lights, but then again, it would ruin the mystical ambience of the soft glow of the 'sun' overhead. He might not even need it. A lot of monsters have surprisingly good vision in darkness.

“Hey, Doc,” Sans tries to greet brightly, but there's a discordant note in his voice that asserts itself despite his attempt to sound nonchalant. He sounds...uncertain? Wary? It's strange that he can't even place the emotion, but Sans is usually a laid back sort of person. He doesn't get worked up over small things, like strange solicitations and ominous holes in his memory.

The room is tinged purple. Is the sun tinted that colour? He seems to remember the real sun of the surface world is a yellow dwarf, and that stars don't actually reach the appropriate temperature to burn purple on the visible spectrum.

Gaster extends a hand towards him, and Sans finds himself being drawn forward. His sneakers drag on the floors as if reluctant, but the rest of his body goes along willingly enough. Gaster seems pleased by this. “Are you ready to continue our work?”

“Yeah, about that...” Sans frowns slightly, trying to concentrate. He feels drunk, like all his thoughts have slowed to a numb crawl. He pictures Papyrus's earnest face, and reminds himself of why he came. “What is it that...what were we...?”

He trails off, confused. The question is right there on the tip of his tongue but he can't remember what it was. He feels like that should concern him, but Gaster's expression is gentle, understanding.

“It's okay, Sans,” he says softly, gathering Sans into his arms once the smaller skeleton is close enough. He tilts Sans's head back, his fingers firm under his subordinate's chin. Up close, Sans can see the fangs normally hidden behind the polite curve of his genial smile. “I'll show you what you need to do.”

* * *

He stumbles in, feeling haggard, but not as completely exhausted as last time. Papyrus is waiting up for him again, sitting on the couch, watching MTT's late night viewing.

Sans forces himself to cross the final distance to the couch and all but collapses against his brother's side. “'Sup, bro. You didn't have to wait up.”

Papyrus makes a show of looking affronted. “IT IS COINCIDENTAL. THERE WAS A METATON MOVIE SPECIAL I WANTED TO SEE.”

Sans squints blearily at the screen. He's pretty sure it's showing nothing more than commercials for MTT brand products. “Sure thing, Pap.”

Papyrus scowls, abashed, his gaze darting away. “BUT THANK YOU FOR MESSAGING ME TO SAY YOU WOULD BE LATE. LAST TIME I WAS CONCERNED.”

“I...huh.” Sans doesn't remember doing that. He discreetly pulls out his phone, blearily trying to focus on the shifting text. It reads; _Papyrus I will be returning late tonight. I have work to complete._

He doesn't usually bother to capitalise when he texts, and there's a noticeable lack of puns. He must have been truly absorbed in his work, but at least he'd remembered. He silently congratulates himself as he shoves his phone back into his pocket.

Papyrus automatically adjusts so Sans can curl up against him, one arm slung companionably over Sans's shoulders. “YOU KNOW, BROTHER, AS MUCH AS I CAN ADMIRE YOUR NEW WORK ETHIC, PERHAPS YOU SHOULD...TAKE IT EASY? I'M WORRIED...”

Sans can't hear him. He's already asleep.

* * *

The days pass by in a haze. Sans knows he must be working harder than he ever has in his life. Hours blur together in a slurry of exhaustion even though he's no longer staying up all night working through his theories. He can hardly keep his eyes open at home; it's like whenever he returns some enormous weight lifts from him, some primal tension unwinding in his soul, and most nights the most he can manage is to crawl into bed in the relief of safety.

Though it hardly makes sense to think of it that way because he knows he's _happy_. He's doing excellent work – Gaster tells him so frequently, smoothing down the furrows in Sans's brow and cradling him in that tingling blanket of magic that's become so familiar. Sans isn't sure how he can be doing well when he can hardly concentrate enough to do simple addition, and all his reports are near illegible from the shaking of his hands, but surely his boss wouldn't coddle him with false praise. Their collaborative project must be going exceptionally well, Sans supposes, only he never really manages to recall what exactly it is that they've been working on.

It must be incredibly important, though. That's the only possible justification for what an inadequate brother he's being to Papyrus, which should always have been his first priority. More and more often, Gaster asks Sans to stay late. At least Sans somehow keeps remembering to text, although the messages have become short, almost curt at times. Sans looks at his phone's history and the words feel like that of a stranger.

He tells himself he just needs to try harder, so even though Gaster invites him to stay back again (and Sans really wants to, he desperately wants to, he needs-!) he manages to stammer out an excuse before his body can betray him and flees home. He shuts the door, and bolts it, and then spends an absurd minute wondering whether he should stack something against it just to be sure.

Papyrus finds him like that several minutes later while Sans is still lost in thought, and seems delighted. “BROTHER! YOU'RE HOME EARLY!”

“Yeah, I...” He has to forcibly turn his attention away from the door. He doesn't know exactly why it's bothering him. It's easy to find a smile for Papyrus, though, even if it's accompanied by a bitter-sweet pang. He's missed his brother. “Sorry, bro. I know it's been a while. I thought maybe tonight we could hang out? Do bro things?”

Papyrus's eyes light up with a sparkle. “YOU MEAN...BROTHERLY BONDING? REALLY?”

Sans chuckles. “Sure, Pap. Movie night? You can pick the channel.”

There's only one to choose from, but Papyrus seems honestly thrilled. “JUST LET MAKE DINNER!”

It's been a while since they've been able to eat a proper meal together. Usually Sans just reheats some of the innumerable leftovers in their fridge. Apparently today warrants a special occasion, however, because Papyrus bustles around the kitchen with intensity and in a surprisingly short amount of time there's some garlic bread (only slightly charred) to go along with the usual pasta (somehow also slightly charred).

“Looks great, bro,” Sans tells him, and he doesn't even need to lie because his brother's cooking skills do seem to be improving, albeit slowly. He reaches for the plates, ready to juggle them on his way to the living room.

“THE DISH WITH THE BREAD IS STILL HOT!” Papyrus scolds him, hurrying over before Sans can do himself any damage. He reaches over his smaller brother with his own gloved hands, pressing up against Sans's back. “HERE, LET ME-”

It's impossible to tell who's more surprised when Sans lets out a gasp of panic and shoves the table so hard it flips over in his attempt to get away. He's shaking, not just his hands this time but his whole body. His skull hurts. A high-pitched, ragged noise tries to work its way out of his throat; the prelude to a scream.

“W-WHAT? BROTHER, WHAT'S-!?” Papyrus takes a half step forward, his face full of loving concern, but Sans is reacting blindly to his height, to his closeness. With a snarl, Sans turns his brother's soul blue and shoves him back up against the opposite wall.

Sans wants to-! He wants...what is he doing again? He grips hard at his collarbone, its subdued ache blooming into a sharper, distracting pain. He looks at the shattered dishes and spilled food spread across the floor without really seeing any of it. There's something much more important he's forgetting, the same thing that's been building inside him, that made him push his brother away in fear, and it's-!

Ah. He's supposed to be at the Lab. What is he doing at home? Gaster will be waiting for him, and he doesn't like to leave his boss waiting.

“I have to...I have to go,” he says, waving a hand vaguely in his brother's direction, releasing the hold on his soul. Why was he doing that anyway? He shouldn't be using that kind of magic on his brother. “Sorry, Pap, I think I...left something at the office.”

That's right. He left something important behind. His important work. How could he forget?

“SANS, WAIT!”

He pulls open a shortcut in the shadow of the kitchen doorway and steps through it. That proves to be the limit of his endurance as the moment he reaches the other side, his legs collapse out from under him and he falls to the floor in a heap.

* * *

“I shouldn't have...I didn't mean to...”

“Hush,” Gaster murmurs, gently fingering the vertebrae of Sans's nape.

Sans is limp across his lap. He doesn't remember how he got there. He doesn't understand the words his mouth is saying. He just knows that he's wrapped up in Gaster's power and it's helping to keep him safe, keep him calm. As long as he's here, he knows everything is going to be okay.

He lets out a little sigh as Gaster's spiderlike fingers crawl along his collarbone. It was hurting again, more so than earlier, but the gentle caress seems to drain away the ache. It makes it easy to ignore the odd dripping of fluids slowly trailing down his ribs.

“Go home and apologise to your brother,” Gaster advises, kind and patient as a mentor. “It's understandable that you're stressed. Your work is very important.”

“My work is very important,” Sans repeats monotonously. Purple hazes his vision.

“Tell him that he needs to be more understanding,” Gaster continues, holding Sans closer, nuzzling at his temple. “He's grown now. He doesn't need you to take care of him. Don't let him come between us.”

“I won't let him come between us,” Sans agrees, though the words taste acrid on his tongue.

_**OR ELSE.** _

The booming words in his skull voices what Gaster does not. Sans nods compliantly. He understands.

* * *

“S-SANS? I THINK WE NEED TO TALK.”

He doesn't think he's ever seen Papyrus look so hesitant, which concerns him in the dim, distant way he's come to regard his brother. Things have been better since their talk. Papyrus leaves him alone most of the time now, and doesn't say anything even when there's no messages from Sans's phone warning that he'll be home late.

He knows how he's meant to respond, though. He smiles for his brother, a forced rictus of a grin. “What's up, bro?”

“I JUST...I KNOW YOUR WORK IS VERY IMPORTANT AND THEY NEED YOU AT THE LAB, BUT--”

Sans watches him struggle for words. His own expression remains blank. It's hard to remember how to keep his face relaxed so it looks friendly and natural. Even his skeletal grin seems to turn down at the corners these days.

Papyrus finally gathers his courage. “SANS, I AM WORRIED ABOUT YOUR HEALTH.”

“What?” Is a laugh appropriate here? Sans thinks it is. He rasps dryly, the sound rattling in his chest. “I don't know what you're talking about.”

Papyrus stares at him beseechingly. “BROTHER, WHAT HAPPENED TO YOUR ARM?”

“Huh?” Sans lifts up the offending limb, noting that the bandages have slipped out from under his sleeve again. “Just a little accident at work. I told you that already.”

“AND YOUR SHOULDER?” Papyrus persists.

The ache in his collarbone is so bad some days he can barely move his arm. It's pretty inconvenient, given that he's left-handed. “It's been funny for a while. I must be getting old...”

“WHAT ABOUT YOUR HP?” Papyrus is trembling. Sans doesn't understand why. “BROTHER, IT'S...IT'S GONE DOWN A LOT. YOU KEEP TELLING ME YOU'RE HAPPY AND THAT YOU LIKE YOUR JOB, BUT--”

“It's rude to check someone's stats without asking, Papyrus,” Sans's mouth says coldly. He's not quite sure that's his voice coming out of it. He's never used a tone like that with his brother.

“I KNOW, BUT...BUT SANS, YOU'RE NOT SLEEPING AND YOU'RE NEVER HOME AND YOU DON'T TALK TO ME AND I KNOW YOU TOLD ME NOT TO BOTHER YOU BUT I'M REALLY AFRAID YOU'RE FALLING DOWN!” Papyrus takes a deep gasp of air and keeps right on ranting before Sans can get a word in. “AND I CAN'T BELIEVE THAT YOUR COWORKERS AND YOUR BOSS HAVEN'T NOTICED SO I AM FORCED TO BELIEVE THAT THE ROYAL LABORATORY DOES NOT ENCOURAGE A HEALTHY ENVIRONMENT AND I REALLY THINK YOU SHOULD QUIT.”

Sans barely hears anything except for the last word. His eye sockets go dark. “Quit?”

“PLEASE, SANS, PLEASE,” Papyrus begs, tentatively moving closer, but Sans steps back out of reach. “YOU'RE HURTING YOURSELF. YOU ONLY HAVE 5HP LEFT, PLEASE-!”

Only 5? That was much worse than even Sans's most pessimistic estimations. His HP has never been high to begin with, but to have fallen so low is absolutely dangerous. For anyone else, Sans would be convinced they were falling down too.

Unfortunately, it didn't matter.

“I can't leave, Papyrus,” he tells his brother gently. “They need me.”

Gaster needed him. He told Sans so frequently. He said Sans was special, that he was different.

“IT'S NOT WORTH THIS!” Papyrus wails. There are tears in his eyes. Sans feels something in his soul fluttering, like a butterfly beating its wings fervently against the cage of his ribs. He ignores it with the ease of practice.

“You're being childish,” Sans's mouth says again without his expressed consent. “This work might free us from the Underground. It's more important than a few points of health.”

Papyrus stares at him silently, tears pouring from his sockets, and somehow that's worse than his protests. Sans can't bear to look at it. He turns away. “I'm not quitting. You'll just have to grow up, Papyrus. I'm going to bed.”

When he's asleep, the purple floods his dreams and steals away all guilt and conscious thought, but tonight he struggles to find any peace. The image of his brother haunts him, and he hates it.

* * *

It's difficult to drag himself into work the next day. He appreciates that the other scientists give him plenty of space as he takes his place at his desk, working through the latest schematic with a dull focus. It's strangely quiet...except, no, it's not strange. Sans had been the one making conversation, telling jokes, trying to liven things up. Now the lab is peaceful again, everything working in perfect synchrony, like the model solar system in Gaster's lab.

He feels the summons like a hook in his soul, silently reverberating through his body. He drops his pen, the final word smearing into an undecipherable scribble. His lab partner nods understandingly and obligingly picks up the drawings for himself, continuing where Sans left off. It's important work, but not as important as this.

Gaster needs him.

He's waiting in the lab, as usual, the room awash with the effortless blanket of his power. Sans isn't certain if he was less aware of it before, or perhaps Gaster has grown in power since he began to sup from his newest acolyte. It's almost overwhelming to be near him, but Sans is shaking from a need so deeply woven into him he can't tell if it's Gaster's or his own. He stumbles forward on uncertain legs and practically falls into Gaster's arms, going limp with relief.

“Ah, my poor boy, I'm sorry,” Gaster murmurs against him, his long-fingered hands stroking over Sans's shoulders, his spine with a care that doesn't entirely mask his hunger. “Just one more night, I promise. Then you can rest.”

Sans nods agreeably, limp and compliant as Gaster unbuttons his labcoat and carefully lifts Sans's shirt. The bite marks scattered over his ribs are mottled and ugly, all in various stages of healing. His collarbone has born the worst of it, but there are deep gouges along his spine, at his wrist, and even on his femur. He knows Gaster would have preferred to go for his throat, but Sans's preferred attire just wouldn't be sufficient to cover it. In a deeply buried, unsubverted corner of his mind, Sans is grateful.

“Hmm...” Gaster considers his options, perching Sans on top of the desk to better examine him. The delicate graze of his hands over Sans's bones elicit a small shiver. The wounds don't hurt, most of the time. Gaster's bite leaves him numb, and the cloud of his mind subdues most sensations except those Gaster wants him to experience. Right now, his focus is on pleasure, and so Sans squirms and flushes, his soul beating weakly. He's too drained to really _want_ it, but Gaster seems intent on making him feel regardless.

“Here, I think,” Gaster eventually decides, running his thumb along Sans's other collarbone. It had escaped any attention so far if only because Gaster was still trying to leave him with at least one functioning arm, but his attentions have become more reckless, less restrained. In the heat of the moment, he tells Sans how unique he is. How young and powerful and delicious. How his presence in the lab has strained Gaster's impressive self-restraint. How, if Sans didn't have a brother to return to, Gaster would just keep him, forever and ever and ever-

Sans makes a small sound that might have been confused for a protest, if Gaster still allowed him such freedoms. The elder scientist chuckles in good humor. “Don't worry. I'll be gentle.”

He presses close, sidling up between Sans's legs, supporting his assistant's back as Sans arches his spine and offers his collarbone. He sighs softly as Gaster's teeth close around it, softly at first, just as he promised. His tongue curls around the bone, warm and wet, making Sans whimper. The sound seems to snap Gaster's reserve. His jaw clenches fiercely as he bites down hard. Sans jerks against him, crying out, but the pain lasts only a fraction of a second before the euphoria swallows his senses. He's keenly aware of Gaster's possessive hold on him, of the heat of his mouth, of the way his own soul struggles and cries out before giving up and allowing Gaster to draw out the flow of magic and marrow as he greedily drinks.

It feels so unbearably good. Sans is dimly aware of the way his chest heaves for unnecessary air, his legs kicking mindlessly as he groans. He can feel the curve of Gaster's mouth as he leers and runs his other hand down Sans's spine, encouraging the noise. The door is open, but no one will interrupt. Everyone understands what it is Sans is doing here, and no one will defy Gaster's authority.

The startling rap against the door manages to take them both by surprise. Gaster jerks back, red and cyan fluids dripping from his mouth in a rare show of impropriety. Without his hold to brace Sans's back, the skeleton drops back on the table like a puppet with cut strings, blinking slowly, almost insensate. He can feel Gaster's attention turning, his tight hold on Sans's mind easing slightly now that he knows his favourite is freshly drained and exhausted.

Gaster wipes his face clean with as much dignity as he can muster. “Enter.”

It's two other members of their team, dull-eyed and expressionless save for the faint twitches that might betray nervousness at interrupting their master.

Between them, caught between a sharp-clawed grip, is Papyrus.

“Intruder,” says one in a flat voice.

“As you expected,” says the other, who Sans faintly remembers successfully sharing a joke with, once. They cast a quick, furtive look at Sans who is still trying to process what it is Papyrus is doing here. He should never be here. A low, incoherent protest burbles out of him, and Papyrus stares wide-eyed.

“SANS!” he tries to lunge out of his captor's hold, but even with all his strength he doesn't succeed. A select few of Gaster's most loyal followers are endowed with a fraction of his unholy strength. Sans hears the faint sound of bones creaking under pressure, and Papyrus yelps, subsiding.

“Ah yes. Finally we meet,” Gaster says, his composure restored. Sans can't see his expression but he feels nothing but dread at the pleasant timbre of Gaster's voice. “Hello, Papyrus. Are you here for your brother? I'm afraid he's indisposed. You see, you interrupted us in the middle of a very important meeting.”

Sans wants to get up but his spine is as limp as overcooked pasta. He can only make a soft hiss of protest as Gaster leans over him and pulls him upright, bracing Sans against his own body so Papyrus can see his brother properly; shirtless, strengthless, still bleeding from the new indents in his collarbone. Papyrus's expression of horror is devastating.

“B-BROTHER...WHAT...” Papyrus gapes, but his shock is quickly morphing to anger. “ _What did you do to him_?”

“Many things,” Gaster goads him. “You see, I am a monster of particular appetites...and your brother is one of the few who can satisfy me.”

His hand closes around Sans's neck, forcing his skull upwards, and Sans has no choice but to comply as he'd forced into a deep, hungry kiss. He can taste his own magical residue on Gaster's tongue, sweet and intoxicating. The heady taste distracts him from the way Gaster's rarely-revealed claws scrape against his vertebrae and the way Papyrus is shrieking, “STOP IT! STOP, LET HIM GO!”

“ _You_ should have let him go,” Gaster says, pulling back with a snarl. “I gave you many chances. I would have let you live, but you have come here, to my territory, to try and take what is _mine_ -!”

Anger makes his hold weaken further, and Sans shakes his head, trying to dislodge the heavy feeling of Gaster's influence clinging to the inside of his skull. He turns his head, watching with growing dread as a cloud of rage storms over Gaster's features before rapidly evaporating, leaving nothing but smooth, placid calm in its wake. “I'm afraid my patience has grown thin, as of late. No need to worry about your brother. I will take excellent care of him in your stead.”

He sets Sans down carefully and takes a half-step towards Papyrus only to be halted in place by Sans's small hand clenching furiously in the front of his lab coat. It takes every ounce of his willpower to hold Gaster there, and even more from reserves he hadn't even imagined he could posses to say, “Don't.”

_Please, please, I'll do anything you want, I'll stop fighting, I'll come willingly, just like you wanted, please-!_

He knows Gaster can hear him still, those nearly-buried thoughts that are still _him_ , that spend most of their time screaming in rage and frustration. Gaster gives him a fond look and gently pries Sans's weak hand from his clothes.

“Remember, you're the one who allowed it to come to this,” he tells Sans sweetly, sincerely, as he steps towards Papyrus, his magic unfurling, filling the room with a thick haze of violet.

He can see Papyrus fighting hard (just the way he did, the first time) but Gaster is freshly fed and has decades, if not centuries of experience in subduing a monster's will. The monsters holding Papyrus release him, but instead of the violent outrage of before, Papyrus sways on his feet, soft-eyed and confused. Gaster's harmless guise unravels, and for a moment Sans sees him without the bewitchment clouding his vision. There's something dark and shapeless, formless and wrong hiding in the deceptive shell of Gaster's body. Something ageless and terrifying.

But when Papyrus turns his gaze on Gaster, Sans can only see captivated wonder in his brother's expression. It seems to give Gaster a moment of pause, and he gently cups Papyrus's face, taking a moment as if to commit it to memory.

“Such a waste,” he laments, winding an arm around Papyrus's waist, pulling him close. “If either one of  you had been willing, I might have been able to keep you both. As it stands...”

He dips Papyrus back in a disturbingly sensual looking embrace. Sans can see the delicate curve of the cervical vertebrae as Papyrus leans his head back, gaze blank, offering his throat. Gaster's fangs seem to elongate, growing larger, sharper. At the very last moment Papyrus manages to make a small, strangled sound of fear as Gaster bits down into his spine.

Sans jerks, adrenaline and terror making his bones twitch. “N-no!”

But he can't move. Gaster has taken too much from him, too often. He knows his HP has trickled down to positively dangerous levels. His collarbone is still bleeding. If he struggles too hard he's going to dust.

He doesn't care.

Papyrus is jerking, whimpering in Gaster's embrace, and Sans knows that Gaster could make it painless, make it pleasurable, but he isn't even extending such a small mercy to his brother. Face contorting in fury, he locks his gaze onto the small glimmer he can see of Gaster's soul, channelling all of his repressed rage in a coiling tendril of magic, and yanks as hard as he can.

In an ideal world, he'd love to tear Gaster's soul in half. The most he manages is to turn in blue and drag it forcibly from Gaster's chest, making him roar in shock, fangs retracting from Papyrus's throat. He manages to pull the soul only a handspan from its owner before it violently resists him, and his shaky hold fails. His vision blurs, eyelights spluttering. That's all he can do. It's not enough.

Except Gaster's cruelty has betrayed him. He allowed Papyrus to regain his coherency, and the last thing Sans sees before his sight gives out is Papyrus jerking his head to the side and biting down on the exposed soul as the only retribution he can he can offer whilst Gaster is still holding him pinned.

The resulting scream is unbearable.

So is the pain. They all feel it; every member of the lab through their connection to Gaster. Sans shrieks and convulses, feeling the echo of that horrible crushing reverberating through his soul. He sobs, thrashing blindly, barely registering that he's no longer lying down. He's in his brother's arms, held tight enough to jostle with each sprinting step Papyrus takes. He doesn't know where they're headed, but the further away he is from Gaster, the more his head begins to clear. He can almost make out the words Papyrus is murmuring to him, fast and panicked, slurring in pain, possibly from the still-leaking gouges on his throat. Sans tries to answer but he's so, so tired.

He shuts his eyes, and when he opens them again, it's to thick, muggy darkness.

They're in Waterfall, he thinks. The ground beneath him feels soft and slightly wet. Water falls from the ceiling, splashing on his face, and for the first time in weeks he can feel it properly. He touches his face, feeling the dampness on his fingers – _his_ fingers, _his_ body, it's _his_ again, goddamnit – and suddenly he's forced to breathe into his palms, hyperventilating, shuddering from the memory of Gaster's teeth all over his body, biting, taking, _painpainpain_ -!

Where is Papyrus?

The instinct to find his brother proves more powerful than his panic attack. Sans looks around, deathly afraid he might discover he's lying in a pile of soggy dust, but Papyrus is curled up not far away in a tight ball. He's shaking too.

“Pap,” he rasps quietly, dragging his body closer. He tentatively puts a hand on Papyrus's shoulder. It's the same wrist Gaster had bitten. He forces himself not to look at the bandages, gritting his teeth. “Bro?”

“S-sans,” Papyrus stutters, his voice unusually subdued, but at least he's awake. Sans nearly collapses in relief. “Sans, it h-hurts, it hurts so much.”

His eyesockets sting from restrained tears. Sans valiantly holds back his own sniveling. “It's 'kay, Pap. It gets better. It fades.”

“No,” Papyrus mourns, sounding wretched. “Brother, I...I don't think it will.”

He turns to face Sans, and the smaller skeleton goes absolutely still. Papyrus's eyelights are glimmering with faint violet light, and his row of perfect, straight teeth is now marred by the slight indent of fangs where his canines should be.

“Sans,” Papyrus says weakly. His eyes are on Sans's collarbone. He swallows visibly. “Sans, I'm...hungry.”


End file.
